1. Field of the Invention
The invention relates to a system having a cordless connection between a modem in a computer and a telephone land line, and more particularly to allowing multiple units and yet maintaining security of each connection.
2. Description of the Related Art
Mobile computers, particularly laptop computers and notebook computers have become increasingly popular. They have performance and capabilities near that of a desktop unit, and if color active matrix liquid crystal displays are utilized, the display is as good as a desktop unit. When combined with the mobility, the popularity is quite understandable. However, one problem with using portable computers is that often they need to be connected to various equipment. For example, when located in a office, it is desirable to connect to various office wide items or non-portable items. For example, a network interface is often necessary, as is a SCSI port for use with various external devices such as CD-ROMs. This situation has conventionally been handled using expansion bases, which contain expansion cards for network and SCSI use and connections for a video monitor, a printer and a full size keyboard, or port replicator strips, which are used to simply provide the connections to the monitor, printer and keyboard without the need for expansion cards.
One of the computer applications which is becoming prevalent is electronic mail or E-mail. The modern business often has a local area network (LAN), with E-mail and appointment calendar applications. A remote user, such as the laptop user away from the office needs to check periodically to maintain in full contact. Thus, a very common addition to a portable computer is a modem to allow remote access to the LAN or other dial up services. Typically this modem is installed in the laptop computer, not directly in any expansion base. So while an expansion base or port replicator may alleviate certain wiring problems, as the various cables need not be disconnected or connected when removing or installing the portable computer, it does not resolve the wiring concerns in the case of a modem, where a separate telephone line is still required to be plugged and unplugged into the modem in the computer. This results in aggravation for the user. Further, this phone line is yet another of the tangled mass of cables utilized with the modern computer. While the monitor, keyboard and SCSI cables are generally located right next to the computer to interconnect the various components, the telephone line often has to be strung across an office and thus is either unsightly or very difficult to route. This is a further drawback to standard conventional modem communications where the modem is contained in the personal computer, be it a laptop or a desktop unit.
Thus the use of a modem in a laptop computer results in aggravations for the user and additionally requires unsightly and cumbersome cabling. Therefore it is clearly desirable to simplify both the laptop portability concerns and the unsightly wiring problem.
The present invention relates to a cordless modem system where a mobile station unit (MSU) is located in the computer or connected to the computer and a base station unit (BSU) which is connected to the telephone line. A radio frequency (RF) link is developed between the two units to allow a cordless connection between the computer and the telephone line. The BSU is completely powered from the telephone line, while the MSU is powered from the computer system. A software protocol is utilized between the two units to open a channel when a call is received or the computer wishes to go off hook. Each MSU and BSU have a personalized identification. The BSU is allowed to perform communications only with authorized and identified MSUs, while the MSU can perform communications only with BSUs with which it has previously communicated. A series of commands are present between the two units to allow the MSU to request a channel, the BSU to grant a channel, the BSU to notify of a ring, and the MSU to request the BSU to go off hook. In addition, there is preferably a command sequence to allow authorization of a particular MSU for use with the BSU.
Preferably, there are two channels in each MSU and BSU, each channel being full duplex. This presence of two channels allows multiple BSUs and MSUs to be utilized in a small area if desired. Once a particular BSU is receiving input or has made a connection with a particular MSU, the BSU is then dedicated to that MSU for the duration of the call. By having two channels, two BSUs can be present in the same environment. Communications between the two units are secure in that the BSUs and MSUs include collision detection logic to determine if both channels are already active. If so, the MSUs and BSUs do not start communication. If a channel is available, an MSU requests that channel, with the request command including the address or identification number of the MSU. The BSU receives the authorization request, checks its list of authorized MSUs and if present and the channel is available, provides a grant command to the MSU. When the BSU receives a call and a ring from the telephone line, after checking for an open channel, the BSU transmits a designated MSU identification along with a ring indication command so that only the specified MSU will answer the call. Further, the grant and ring indication commands include the BSU identification number so that the MSU will communicate only with that particular BSU while the call is on-going. In this manner, one MSU will not intercept the calls for another MSU after the link has been established and a BSU will not provide calls to unauthorized MSUS. This allows data transfer to be secure even though multiple MSUs are present and can generally share a single BSU.
Further, the development of the protocol is such that the communications software utilized in the computer is not even aware of the presence of the cordless connection. Both the MSUs and BSUs contain microcomputers and proper signaling to sense what action is requested from the modem or telephone line and perform the cordless or radio transmission function seamlessly. Thus conventional communication software can be utilized without any particular special commands or structure. This allows the user to continue to use his preferred communication software package.
Two embodiments of the MSU are provided, one configured as an external data access arrangement (DAA) to be connected with laptop modems configured to utilize external DAAs, while in the second embodiment the MSU is incorporated with the modem hardware to provide a single, fully integrated unit. The BSU is a single, preferably relatively small, box which simply plugs into the telephone line.
Thus by having this transparent cordless link, the laptop user does not have to disconnect or connect a telephone line each time he moves his laptop and further the telephone line need not be routed across open areas or through difficult passages.